benchmark.mojo: add time_between measurement type.

apps/benchmark/README.md

Index: apps/benchmark/README.md
diff --git a/apps/benchmark/README.md b/apps/benchmark/README.md
index 10da93e7c3936a9ef9a1ac9df881d20456f4d6e3..8380939b3ce9f370cdde5d1d2221bc4f0d4b2c95 100644
--- a/apps/benchmark/README.md
+++ b/apps/benchmark/README.md
@@ -20,14 +20,22 @@ The following arguments are **optional**:
 
 Any other arguments are assumed to be descriptions of measurements to be
 conducted on the collected trace data. Each measurement has to be of form:
-`<measurement_type>/<trace_event_category>/<trace_event_name>`.
+`<measurement_type>/<measurement_arg_1>/<measurement_arg_2>/...`.
 
 The following measurement types are available:
 
- - `time_until` - measures time until the first occurence of the event named
-   `trace_event_name` in category `trace_event_category`.
- - `avg_duration` - measures average duration of all events named
-   `trace_event_name` in category `trace_event_category`.
+ - `time_until/<trace_event_category>/<trace_event_name>` - measures time until
+   the first occurence of the event named `trace_event_name` in category
+   `trace_event_category`.
+ - `time_between/<first_event_category>/<first_event_name>/<second_event_category>/<second_event_name>`
+   measures time between the first occurence of the event named
+   `<first_event_name>` in category `<first_event_category>` and the first occurence
+   of the event named `<second_event_name>` in category
+   `<second_event_category>`. The measurement will fail if the first occurence
+   of the first event happens after the first occurence of the second event.
+ - `avg_duration/<trace_event_category>/<trace_event_name>` - measures average
+   duration of all events named `trace_event_name` in category
+   `trace_event_category`.
 
 ## Runner script